Method of manufacture of an incandescent lamp

ABSTRACT

A method of manufacturing an incandescent lamp which includes the stretching of a filament, previously clamped to lead wires, by straightening a premeasured bend in one of the lead wires. In a variation of the method, an open spiral filament support is closed around the filament following the stretching process.

United States Patent 1191 1111 3,85%,489 Jarc et ai. Nov, 26, 974

[54] METHOD OF MANUFACTURE OF AN 3,271,093 9/1966 Meier 316/19 3,530,3299/1970 Stone et al 313/278 INCANDESCENT LAMP 3,594,884 7/l97l Siege]29/25.!5 Inventors: Robert J Kent; Fredrick 3,743,375 7/1973 Fraeye316/20 Ritzinger, Parma, both of Ohio [73] Assignee: General ElectricCompany, Primary Examiner-Roy Lake Schenectady, NY. AssistantExaminerJames W. Davie Attorney, Agent, or FirmEmil F. Sos, Jr.;Lawrence [22] Flled' 1973 R. Kempton; Frank L. Neuhauser [211 App]. No.:424,875

1 [57] ABSTRACT [52] U.S. Cl 316/20, 29/25.15, 313/278 51 1m. (:1.111011 j9/38 A method manufacturmg mcandescem lamp 5 1 Fieid f Search H29 2515 313/27 27 which includes the stretching Of a filament,previously 316/17 18 clamped to lead wires, by straightening apremeasured bend in one of the lead wires. In a variation of the [56]References cited method, an open spiral filament support is closedUNITED STATES PATENTS around the filament following the stretchingprocess.

3.007.074 10/196! Swasey et al. 313/278 5 Claims, 3 Drawing FiguresMETHOD OF MANUFACTURE OF AN INCANDESCENT LAMP BACKGROUND OF THEINVENTION 1. Field of the Invention The invention relates generally to amethod of manufacturing an incandescent lamp. More particularly, theinvention relates to a method of stretching a clamped filament to apredetermined length by straightening a bend in one of the lead wires.

2. Description of the Prior Art In the manufacture of incandescentlamps, particularly tungsten-halogen lamps, filament tensioning betweenlead wires and filament location are very-important to lamp life andperformance. Prior art practices included clamping one leg of a filamentto a lead wire and then manually stretching the other end of thefilament until it could be clamped to a second lead wire. This becomesespecially time-consuming if a filament support is used whichnecessitates the threading of the filament through a loop or spiralbefore attaching the filament leg to the second lead. The use of afilament support is one method of preventing the filament fromcontacting the bulb wall.

Efforts to automate the filament mounting process and associatedprocesses of pinch sealing, flushing, filling and tipping have beenunsuccessful because of space limitations created by the lamp geometry.In other words, a means for stretching and tensioning the filament wouldinterfere with the means used to clamp the filament legs to the lead-inconductors. This problem would be further complicated if a filamentsupport were used because a mechanism would have to be provided tothread the filament through a support during or prior to the filamentstretching process.

As previously mentioned, incandescent lamps, especially tungsten-halogenlamps, with improperly positioned and tensioned filaments areundesirable. Too little tension may cause the filament to sag andpossibly fail touching the bulb wall, whereas too much tension may causepremature rupture or fracture of the filament. Filament location is alsoimportant because a fraction of an inch for a powerful light source asis used in tungsten-halogen lamps can cause a substantial decrease inprojected light when the lamp is placed in an appropriate reflector.

SUMMARY OF THE INVENTION It is therefore an object of the invention toprovide a method of lamp manufacture which is adaptable to automatedequipment. A further object of the invention is to provide a method ofproperly stretching the filament in a rapid automatic process. Yetanother object of the invention is to accurately position the filamentwith respect to the remainder of the mount structure. Still anotherobject of the invention is to provide a method for making a mountstructure which contains a filament support but does not requirethreading the filament through the support.

,The objects of the invention are accomplished by providing a leadinconductor with a predetermined bend which eventually is straightened toprovide tension to the filament. In one form of the method or process, aunitary piece of ductile molybdenum wire is provided with a bend and twoclamping ends. This wire is held in a pair of jaws, at least one ofwhich is movable, with the bend positioned between the jaws.

When the wire lead is in position, the unstretched filament is placedbetween the clamping ends of the molybdenum wire with a portion of eachcoil leg extending beyond the clamping end of the lead wires. The clampsare then closed over the coil legs. In the next processing step, one orboth of the jaws move in a direction away from the bend therebystraightening it and stretching the filament to an appropriate length.Unitary molybdenum wire is then severed and each end is attached to athin molybdenum foil portion which in turn is connected to an outer leadwire also generally made of molybdenum. This assembly of leads, foilsand coil is usually referred to as a mount. The mount may contain abridge of quartz material located perpendicular to and near the severedends of the lead wires.

An envelope of vitreous material is placed over the mount and the foilportions are pinch sealed in the envelope. The lamp is then exhausted,flushed and filled with a fill gas mixture containing a small quantityof a halogen. Following this, the envelope exhaust tube is tipped off ina customary manner to form a finished lamp.

In another embodiment of the invention, an open spi ral filament supportis attached at one end to the quartz bridge. The other end containingthe spiral is open and located near the center of the filament.Following the tensioning of the filament, the spiral is closed toprovide support and prevent the filament from touching the bulb wall.

BRIEF DESCRIPTION or THE DRAWINGS FIG. I is aperspective view of a lampmade according to the invention;

FIG. 2 is a perspective view showing an attached, unstretched coil andan open spiral filament support; and

FIG. 3 shows the tensioning of the filament by movement of thestretching jaws and the closing of the spiral.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The particular lamp, 10,illustrated in FIG. I is a 250- watt, l20-volt single-endedtungsten-halogen lamp. It is comprised of an envelope 11, generally ofquartz or other vitreous material of a high silica content, pinch seal12 and mount structure 113. Filament 114 has leg portions 15, I6 clampedto leads I7 and I8 which may be individual leads or leads formed bysevering unitary molybdenum wire 19, shown in FIGS. 2 and 3.

Mount structure 13 is comprised of outer lead wires 20 and 2B, usuallyof molybdenum, foliated portions 22 and 23, also of molybdenum, innerleads I7, 18, bridge 24, support wire 25, and filament I4. Portions ofthis mount structure are shown in FIGS. 2 and 3.

Unitary wire 19, of the illustrated example, is 0.020- inch-diametermolybdenum wire having a tensile strength of between 40-45 kg/mg/200 mm.As illustrated in FIG. 2, filament legs 15 and 16 are clamped by hooks26, 27 which curl back on the lead wires approximately 0.050 inch overthe legs to assure a mechanical and electrical connection. Bridge 24,preferably of quartz, holds wire portions 17 and 18 in fixedrelationship to each other. Portion I8 is firmly held in jaws 28 and 29,at least one of which is movable. Premeasured bend 30 is located betweenthe jaws so that it may subsequently be straightened to impart theproper tension to filament 14. After the mount is secured in the jawswith attached but untensioned filament 14, one or both of the jaws maybe moved in a direction away from the bend as illustrated by arrow 31 inFIG. 3. 1

This movement of the jaw straightens the bend 30 to a degree necessaryto impart the proper amount of tension to the filament. It is notnecessary that the bend be entirely straightened so long as the filamentis stretched to a predetermined length and predetermined tension. Theradius of the bend in the example is 0.187 inch and it stretches acoiled-coil 8 filament from a relaxed legto-leg coil dimension of mm toa tensioned coil dimension of 18 mm. The overall wire length, beforesevering, of unitary molybdenum wire 19, which consists of portions 17and 18, is 1.390 inch of which approximately 0.150 inch will be cut fromthe U-shaped por tion before the inner leads are attached to foils 22and 23. Following the filament stretching operations, unitary wire 19 issevered to form inner leads 17 and 18, as indicated above. The ends ofthe leads are then attached to molybdenum foils 22 and 23 by welding,for example. Foils 22 and 23 are in turn attached to outer leads and 21.to form mount 13.

The mount is placed in a suitable holding device, and envelope 11 isplaced over the mount so that the lower portion of the envelope can bepinch sealed to the molybdenum foils 22 and 23. The next step in theprocessing is to exhaust the envelope through an exhaust tube, theresidue of which is shown at 32. The exhausted lamp is flushed withnitrogen to remove impurities and filled with a gas mixture such asnitrogen, argon and a halogen gas. Both iodine in the form of CH I andbromine in the form of CH Br have been found to be effectiveregenerative cycle agents. After filling, the lamp exhaust tube istipped off as shown at 32 to form a finished lamp.

In an embodiment containing filament support 25, which can be made ofmolybdenum or tungsten, the spiral portion 31 is initially in an openposition, as shown in FIG. 2. By having the spiral portion in an openposition, it is not necessary to thread the filament through the spiralduring the clamping and stretching processes. This technique facilitatesrapid manufacture. After the filament is stretched, the spiral portionis closed around the filament by jaws 32.

Another variation of the invention is the use of separate lead wires 17and 18 in place of unitary wire 19 which is subsequently severed to formleads l7 and 18. In this embodiment, lead 18 would contain bend 30 whichwould be straightened to tension the filament.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

l. The method of manufacturing an incandescent lamp comprising the stepsof:

a. positioning a unitary piece of wire, having two unattached ends and apremeasured bend, in a holding means having at least one movable jaw;

b. aligning the legs of a tungsten filament with the ends of saidunitary piece of wire;

0. clamping the ends of said wire around the legs of said tungstenfilament;

d. moving said movable jaw in a direction away from the bend in saidwire thereby straightening said premeasured bend and stretching saidfilament;

e. severing said unitary wire to form two discrete lead-in conductors;

f. attaching the ends of said discrete lead-in conductors to foliatedportions which are attached to outer lead-in conductors to form a mount;

g. placing an envelope over said mount;

h. pinch sealing said foil portions in said envelope;

i. flushing and filling said envelope with a fill gas mixture; and

j. tipping said envelope to form a finished. lamp.

2. The method of manufacture claimed in claim 1 wherein said holdingmeans has two movable jaws which move in a direction away from eachother to straighten the wire and tension the coil.

3. The method of manufacture claimed in claim 1 wherein a ceramic bridgeis attached to said unitary piece of wire to hold portions of the wirein fixed rela tion to each other.

4. The method of manufacture claimed in claim 3 wherein said ceramicbridge contains one end of a filament support with the other end beingan open spiral located near the center of the filament, closing saidopen spiral around said filament after the filament has been tensionedto prevent said filament from touching the envelope.

5. The method of manufacturing an incandescent lamp comprising the stepsof:

a. positioning two lead wires, one of which has a premeasured bend, in aholding means;

b. aligning the legs of a tungsten filament with the ends of the leadwires;

c. clamping the ends of said wire around the legs of said tungstenfilament;

d. moving the ends of said bent lead wires so that said bend isstraightened and the tungsten filament is stretched to a predeterminedlength;

e. attaching the other end of said lead-in conductors to foliatedportions which are attached to outer lead-in conductors to form a mount;

f. placing an envelope over said mount;

g. pinch sealing said foil portion in said envelope;

h. flushing and filling said envelope with a fill gas mixture; and

i. tipping said envelope to form a finished lamp.

1. The method of manufacturing an incandescent lamp comprising the stepsof: a. positioning a unitary piece of wire, having two unattached endsand a premeasured bend, in a holding means having at least one movablejaw; b. aligning the legs of a tungsten filament with the ends of saidunitary piece of wire; c. clamping the ends of said wire around the legsof said tungsten filament; d. moving said movable jaw in a directionaway from the bend in said wire thereby straightening said premeasuredbend and stretching said filament; e. severing said unitary wire to formtwo discrete lead-in conductors; f. attaching the ends of said discretelead-in conductors to foliated portions which are attached to outerlead-in conductors to form a mount; g. placing an envelope over saidmount; h. pinch sealing said foil portions in said envelope; i. flushingand filling said envelope with a fill gas mixture; and j. tipping saidenvelope to form a finished lamp.
 2. The method of manufacture claimedin claim 1 wherein said holding means has two movable jaws which move ina direction away from each other to straighten the wire and tension thecoil.
 3. The method of manufacture claimed in claim 1 wherein a ceramicbridge is attached to said unitary piece of wire to hold portions of thewire in fixed relation to each other.
 4. The method of manufactureclaimed in claim 3 wherein said ceramic bridge contains one end of afilament support with the other end being an open spiral located nearthe center of the filament, closing said open spiral around saidfilament after the filament has been tensioned to prevent said filamentfrom touching the envelope.
 5. The method of manufacturing anincandescent lamp comprising the steps oF: a. positioning two leadwires, one of which has a premeasured bend, in a holding means; b.aligning the legs of a tungsten filament with the ends of the leadwires; c. clamping the ends of said wire around the legs of saidtungsten filament; d. moving the ends of said bent lead wires so thatsaid bend is straightened and the tungsten filament is stretched to apredetermined length; e. attaching the other end of said lead-inconductors to foliated portions which are attached to outer lead-inconductors to form a mount; f. placing an envelope over said mount; g.pinch sealing said foil portion in said envelope; h. flushing andfilling said envelope with a fill gas mixture; and i. tipping saidenvelope to form a finished lamp.